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use std::alloc::Layout;
use std::any::{TypeId, type_name};
use std::fmt::Debug;

pub use engine_macros::Reflection;

pub trait Reflection: 'static
{
    const TYPE_REFLECTION: &Type;

    fn type_reflection() -> &'static Type
    where
        Self: Sized,
    {
        Self::TYPE_REFLECTION
    }

    fn get_type_reflection(&self) -> &'static Type
    {
        Self::TYPE_REFLECTION
    }
}

#[derive(Debug)]
#[non_exhaustive]
pub enum Type
{
    Struct(Struct),
    Array(Array),
    Slice(Slice),
    Literal(Literal),
}

impl Type
{
    pub const fn as_struct(&self) -> Option<&Struct>
    {
        match self {
            Self::Struct(struct_reflection) => Some(struct_reflection),
            _ => None,
        }
    }
}

#[derive(Debug, Clone)]
pub struct Struct
{
    pub fields: &'static [StructField],
}

#[derive(Debug, Clone)]
pub struct StructField
{
    pub name: &'static str,
    pub index: usize,
    pub layout: Layout,
    pub byte_offset: usize,
    pub type_id: TypeId,
    pub type_name: &'static str,
    pub get_type: FnWithDebug<Option<&'static Type>>,
}

impl StructField
{
    pub fn type_reflection(&self) -> Option<&'static Type>
    {
        self.get_type.get()
    }
}

#[derive(Debug, Clone)]
pub struct Array
{
    pub item_reflection: &'static Type,
    pub length: usize,
}

#[derive(Debug, Clone)]
pub struct Slice
{
    pub item_reflection: &'static Type,
}

#[derive(Debug)]
pub struct Literal
{
    pub layout: Layout,
    pub type_id: TypeId,
    pub type_name: fn() -> &'static str,
}

macro_rules! impl_with_for_literals {
    ($($literal: ty),*) => {
        $(
            impl Reflection for $literal
            {
                const TYPE_REFLECTION: &Type = &Type::Literal(Literal {
                    layout: Layout::new::<$literal>(),
                    type_id: TypeId::of::<$literal>(),
                    type_name: || type_name::<$literal>()
                });
            }
        )*
    };
}

impl_with_for_literals!(
    u8,
    i8,
    u16,
    i16,
    u32,
    i32,
    u64,
    i64,
    u128,
    i128,
    f32,
    f64,
    usize,
    isize,
    &'static str
);

impl<T: Reflection, const LEN: usize> Reflection for [T; LEN]
{
    const TYPE_REFLECTION: &Type = &Type::Array(Array {
        item_reflection: T::TYPE_REFLECTION,
        length: LEN,
    });
}

impl<T: Reflection> Reflection for &'static [T]
{
    const TYPE_REFLECTION: &Type =
        &Type::Slice(Slice { item_reflection: T::TYPE_REFLECTION });
}

#[derive(Clone)]
pub struct FnWithDebug<Value>
{
    func: fn() -> Value,
}

impl<Value> FnWithDebug<Value>
{
    pub const fn new(func: fn() -> Value) -> Self
    {
        Self { func }
    }

    pub fn get(&self) -> Value
    {
        (self.func)()
    }
}

impl<Value: Debug> Debug for FnWithDebug<Value>
{
    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result
    {
        formatter
            .debug_tuple("FnWithDebug")
            .field(&self.get())
            .finish()
    }
}